With reference to FIG. 8 for a conventional toilet tank structure, the structure comprises a toilet tank 50 having a sink 51 and a faucet 52, and the water supply of the faucet 52 is linked with the toilet flushing, so that when a toilet is flushed, the faucet 52 is linked to output water for washing hands after using the toilet, and the waste water produced after washing hands is drained through a drain pipe 53 of the sink 51 and stored in the toilet tank 50. When it is necessary to wash hands without using the toilet, the faucet 52 only supplies water if the toilet is flushed. As a result, the water resource is wasted, and the use is inconvenient. Obviously, the conventional toilet tank requires improvements.